The invention relates to a thermal triggering device for sprinklers for stationary fire-extinguishing systems, with a temperature-dependent safety device which is designed as a glass bulb with a filling and supporting elements, which device until the moment of triggering holds a sealing member of the sprinkler in a closed or blocking position.
The demands made on sprinklers for stationary fire-extinguishing systems are to the effect that increasingly very much shorter triggering times are demanded in order to be able to fight fires arising more quickly and hence more effectively than before. An essential criterion for the triggering time of a sprinkler is the triggering inertia of its thermal triggering element, which is designed as a safety device. In relevant circles, the so-called RTI value has become internationally accepted as a measurement for the triggering inertia, RTI standing for the expression "Response Time Index", i.e. for the "inertia index". The RTI value is the time constant for the heating-up of the triggering element which occurs in an air current at a rate of 1 m/s. It is calculated according to the formula EQU RTI=.tau..multidot.u.sup.1/2,
whereby
.tau.=heat storage capacity/heat absorption capacity=triggering inertia and
u=the speed of the burnt gas PA1 u is the speed of the burnt gas in m/sec, PA1 .DELTA.Tg is the temperature of the burnt gas minus the pipe temperature (.apprch. water temperature) in .degree.C. PA1 .tau. the time constant of the triggering element at a given speed of the burnt gas in sec PA1 RTI .tau..multidot.u.sup.1/2 in sec .multidot..sqroot.m/sec and PA1 C is the parameter for the heat transfer by conduction of heat from the triggering element to the piping in .sqroot.m/sec.
and the heat storage capacity is defined as the required quantity of heat per .degree.C. temperature increase measured in cal, kcal or Joules and the heat absorption capacity which is dependent on the air speed is defined as the total quantity of heat, measured in cal/sec, Joules/sec or also watts, flowing towards the triggering element from the surrounding air per .degree.C. temperature difference between them per unit of time, e.g. per second.
In conventional sprinklers, this time constant is approximately 200 to 400 seconds. More recent developments of triggering elements which are designed as glass bulbs have far lower time constants, which are about one-fifth of the stated values. Such glass bulb triggering elements are described, for instance, in German patent No. 32 20 124 and in European patent application No. 0 215 331.
In German patent No. 32 20 124, the triggering time of the sprinkler is shortened by a solid insert which is arranged as is known in the glass bulb and acts as a displacement member being produced from a material, the heat capacity of which is lower than the heat capacity of the expansive liquid in the glass bulb, the volume of the expansive liquid in the glass bulb being decreased by the displacement member without the glass member having its dimensions changed and therefore being altered in its physical properties.
In contrast to this, in European patent application No. 0 215 331, a glass bulb which can quickly respond in accordance with the new requirements without considerable loss of strength and continuous loadability, one strives to thicken at least one end of the glass bulb with respect to the thin shank and give it a larger diameter than said shank.
In these two cases, one attempts to achieve the decrease in triggering inertia and hence the reduction of the triggering delay of the sprinklers by special formation of the glass bulb or its filling.
However, not only the magnitude of the triggering inertia RTI is decisive for the extent of the triggering delay of the sprinklers, but also another value, namely the so-called C-value, which is characteristic of the triggering delay as a result of the dissipation of heat from the triggering element via the sprinkler connection to the water-filled piping.
According to Document N 139 in ISO TC 21 SC 5 WG 1 by Gunnar Heskestad and Robert G. Bill, the temperature increase in the triggering element can be determined according to the formula ##EQU1## whereby .DELTA.Te is the temperature of the triggering element minus the pipe temperature (.apprch. water temperature) in .degree.C.,
This formula can be used to demonstrate the temperature gradient in the triggering element and thus the triggering delay at different speeds of the burnt gas and burnt gas temperatures. Thus it can be used to demonstrate that the RTI value is the dominating parameter if there is a high supply of energy, for instance when there is a high speed of burnt gas and also a high temperature difference between the burnt gas and the triggering element.
This formula can also be used to demonstrate that the C-value is the dominating parameter if there is a low supply of energy, for instance when there is a low speed of burnt gas and also a small temperature difference between the burnt gas and the triggering element, and the C-value therefore has a great influence. The influence of the C-value may in this case be so large that the triggering element no longer responds, although the burnt gas temperature is considerably above the intended triggering temperature of the triggering element. In the case of fires which develop slowly, the triggering of the sprinklers is thereby prevented for a long time, i.e. greatly delayed, although the required value of the fire parameter "temperature" which is intended to trigger the sprinklers has already obviously been reached for some time or has even been exceeded, with the consequence that the fire can develop and spread to an unnecessarily large extent and thus unnecessarily extensive damage occurs before the fire-extinguishing system becomes operative, the C-value therefore has a great influence.
A high C-value may however also prove disadvantageous if, in the case of normally or rapidly developing fires and sprinklers mounted at a great height on the ceiling of the room, as a result of the mixing of the burnt gases with the surrounding air, a low burnt gas temperature and a low speed of burnt gas occur. The opportunity of fighting and thus safely extinguishing the fire at the earliest possible time is lost here as well.
Using investigations into a series of sprinklers which are common at present, inter alia those according to German patents Nos. 25 39 703 and 26 39 245, in a current of air at a speed of 1 m/s and with a temperature increase of approximately 0.5.degree. C. per minute, and with a threaded connection of the sprinklers through which water flows at a temperature of approximately 20.degree. C., i.e. in a test layout which fully corresponds to real fire conditions, it was noted that the sprinklers were only triggered at temperatures which were considerably higher than their nominal triggering temperatures. However, this means nothing other than that the known sprinklers require too long a time before they respond, so that fighting the fire in good time is jeopardised at least and thus there is a danger of unnecessarily extensive fire damage.